This invention is generally directed to processes for the preparation of squaraine compositions, and more specifically to economical processes for the preparation of symmetrical and unsymmetrical squaraines wherein the selection of the costly squaric acid reactant is avoided. In one embodiment, the present invention is directed to the preparation of unsymmetrical and/or symmetrical squaraines by a cycloaddition, reductive alkylation and condensation method thereby avoiding the use of costly squaric acid as a reactant. In another embodiment of the present invention, there are provided symmetrical, or unsymmetrical squaraines with improved xerographic properties, inclusive of high charge acceptance, low dark decay, high photosensitivity, and improved cyclic stability when these compositions are incorporated into photoconductive imaging members. Also, in another embodiment of the invention of the present application there are provided imaging members with photoconductive layers comprised of the squaraines obtained with the processes illustrated herein, and charge or hole transport layers, especially those comprised of aryl amines, which members are sensitive to light in the wavelength region of from about 400 to about 1,000 nanometers. Therefore, the resulting members are responsive in some embodiments to visible light, and infrared illumination originating from laser printing apparatuses wherein, for example, gallium arsenide diode lasers are selected. The photoresponsive imaging members of the present invention can also, for example, contain situated between a photogenerating layer and a hole transporting layer, or situated between a photogenerating layer and a supporting substrate with a charge transport layer in contact with the photogenerating layer, a photoconductive component comprised of the unsymmetrical squaraines illustrated herein.
Numerous different xerographic photoconductive members, including squaraines and processes thereof, are known including, for example, or a composite layered device containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described, for example, in U.S. Pat. No. 3,121,006, wherein there are disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. Also, layered photoresponsive devices including those comprised of separate generating layers and transport layers are described in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference, and overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin are illustrated in U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain aryl amines as mentioned therein. Also, there is illustrated in U.S. Pat. No. 4,415,639, the disclosure of which is totally incorporated herein by reference, the use of known squaraine compositions, such as hydroxy squaraines, as a photoconductive layer in an infrared sensitive photoresponsive device. More specifically, there is described in this patent an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interfacial layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which photoconductive composition is selected from various squaraine compositions, including hydroxy squaraine compositions, and a hole transport layer. Other patents disclosing photoconductive devices with squaraines, and processes for the preparation thereof usually with squaric acid are U.S. Pat. Nos. 4,471,041; 4,507,480; 4,390,610; 4,353,971 and 4,391,888.
There are illustrated in U.S. Pat No. 4,624,904, the disclosure of which is totally incorporated herein by reference, photoconductive imaging members with unsymmetrical hydroxy squaraine compositions, and aryl amine hole transport layers. The aforementioned unsymmetrical squaraine compounds can be obtained, for example, by the initial preparation of an aryl cyclobutenedione intermediate, followed by the reaction thereof with a substituted aniline. More specifically, with respect to method A illustrated in the '904 patent, the aryl cyclobutenedione is prepared by heating with reflux at a temperature of from about 40.degree. to 50.degree. C., depending on the solvent selected; about 20 millimoles to about 50 millimoles of substituted aniline; from about 60 millimoles to about 150 millimoles of dihalocyclobutenedione; and from about 100 milliliters to about 1,000 milliliters of a Fredal Craft solvent inclusive of, for example, carbon disulfide nitrobenzene or methylene chloride. This reaction is accomplished in the presence of from about 200 to about 900 millimoles of a catalyst such as aluminum chloride, and the resulting substituted aniline is reacted with a hydroxy substituted aniline in the presence of an aliphatic alcoholic solvent. Subsequent to separation, there are obtained the desired unsymmetrical squaraine compounds of the formula as detailed on page 8, beginning at line 10, for example.
Additionally, there are disclosed in a number of patents processes for preparing squaraine compositions. For example, in U.S. Pat. No. 4,524,220 there is illustrated a squaraine process by the reaction of squaric acid, and an aromatic aniline in the presence of an aliphatic amine. Also, in U.S. Pat. No. 4,524,219 there is described a process for the preparation of squaraines by the reaction of an alkyl squarate, and an aniline in the presence of an aliphatic alcohol and an optional acid catalyst. Moreover, disclosed in U.S. Pat. No. 4,524,218 are processes for the preparation of squaraines by the reaction of squaric acid with an aromatic amine, and a composition selected from the group consisting of phenols and phenol squaraines, which reaction is accomplished in the presence of an aliphatic alcohol and an optional azeotropic catalyst. Other processes for preparing squaraines are illustrated in U.S. Pat. No. 4,525,592, wherein there is described the reaction of a dialkyl squarate, and an aniline in the presence of an aliphatic alcohol and an acid catalyst.
Other references of interest include U.S. Pat. Nos. 3,617,270; 3,824,099; 4,175,956; 4,486,520; 4,508,803; 4,585,895; 4,521,621; 4,559,286; 4,552,286; 4,552,822 and 4,624,904.
As a result of a patentability search, there were selected U.S. Pat. No. 4,585,895 and Japanese 62-249952, which discloses the use of hydroxycyclo-butenedione derivatives as synthetic intermediates for squarylium compounds.
In U.S. Pat. No. 4,521,621, the disclosure of which is totally incorporated herein by reference, there are described photoresponsive imaging members containing unsymmetrical squaraines comprised by forming a mixture of squaric acid, a primary alcohol, a first tertiary amine, and a second tertiary amine. Also, in U.S. Pat. No. 4,886,722, the disclosure of which is totally incorporated herein by reference, a cycloaddition-condensation reaction for the preparation of certain squaraines is illustrated. More specifically, there is illustrated in the aforementioned patent the preparation of unsymmetrical squaraines by condensing, for example, a 1-alkoxyaryl-2-hydroxycyclobutene-3,4-dione derivative with an N,N-dialkylaniline derivative, such as 1-3', 4'-dimethoxy-phenyl-2-hydroxycyclobutene-3,4-dione and 3-fluoro-N,N-dimethylaniline in a molar ratio of about 1 to 6, and preferably in a ratio of about 1 to 3 in the presence of an aliphatic alcohol, such as propanol, and an optional drying reagent. About 500 milliliters of alcohol per 0.1 moles of 1-alkoxyaryl-2-hydroxycyclobutene-3,4-dione are selected, however, up to about 1,000 milliliters of alcohol to about 0.5 to 1 moles of 1-alkoxyaryl-2-hydroxycyclobutene-3,4-dione can be selected. The drying reagent can be heterogeneous such as molecular sieves or homogeneous such as a trialkyl orthoformate. A ratio of 1 to 10 equivalents of drying reagent, more specifically tributyl orthoformate, can be used with a ratio of about 1 to 4 to the cyclobutene dione being preferred. Also, the reaction is generally accomplished at a temperature of about 60.degree. C., to about 130.degree. C., and preferably at a temperature of 70.degree. C. to about 100.degree. C. with stirring until the reaction is completed. Subsequently, the desired product can be isolated from the reaction mixture by known techniques such as filtration, and the product identified by analytical methods including IR, NMR, and mass spectrometry. Further, carbon, hydrogen, and nitrogen elemental analysis can be selected for aiding the identification of the product.
Although the above squaraines, and processes thereof are suitable for their intended purposes, there continues to be a need for other processes. More specifically, there remains a need for simple, economical processes for preparing certain symmetrical, or unsymmetrical squaraines with stable properties, which when incorporated into photoconductive devices result in reduced dark decay characteristics, and increased charge acceptance values as compared to substantially similar squaraine imaging members. Moreover, there remains a need for processes that enable the preparation of unsymmetrical and symmetrical squaraines wherein the use of costly squaric acid component reactants are avoided. In addition, there remains a need for photoconductive imaging members with certain stable electrical characteristics, that is for example the aforementioned imaging members are electrically stable for over 100,000 xerographic imaging cycles. In addition, imaging members with the aforementioned squaraines of the present invention are sensitive to a broad range of wavelengths, including visible and infrared light, such as of from about 400 to 900 nanometers, enabling such members to be useful in electrophotographic imaging and printing process including, for example, processes wherein diode lasers are selected.